Update 2:36 p.m. | NEWARK, Del. — The Democratic senator who holds the seat long occupied by Vice President Joseph R. Biden, Jr. has put the Obama administration on the verge of victory on the Iran deal.

Sen. Chris Coons announced on the campus of the University of Delaware Tuesday that he would provide the 33rd vote against a resolution of disapproval for the P5+1 nuclear agreement with Iran. That puts the agreement one vote short of the number needed to sustain a presidential veto.

Coons began his speech to an abundance of local television cameras by expressing concerns about provisions of the deal, including enforcement mechanisms.

"I certainly understand why Delawareans would ask how I could possibly not oppose this agreement. If it has flaws and weaknesses and foreseeable bad consequences, why not heed the vocal opposition of many of my neighbors and friends and join a majority of my Senate colleagues who will oppose it? The answer to that question isn’t easy, and it's not one I have come to lightly," Coons said. "If Congress rejects this agreement, removing the U.S. from the P5+1 process, the path forward is even less clear than it is with the deal."

Coons said he received assurances from the Obama administration about the enforcement and implementation of the agreement before agreeing to support the deal. He said he spoke directly with both Biden and President Barack Obama about the deal.

Coons called the deal the best credible option on the table.

In an interview with a University of Delaware alumnus at The Washington Post ahead of the speech, Coons said a recent conversation with Biden was important in his final decision.

"I got to a place where I wanted the advice and input of Joe," Coons said.

And as more Democratic caucus members announced support, the odds increased that Minority Leader Harry Reid of Nevada and the Democrats would end up achieving the 41 votes needed to prevent the resolution from overcoming a filibuster and advancing through the Senate.

Coons' speech followed the announcement by Sen. Bob Casey, a Democrat from neighboring Pennsylvania, that he to would support the agreement, which brought the tally of Democratic caucus members backing the deal to 32.

"After the more than six weeks of intensive review, I have concluded that I will support the [Joint Comprehensive Plan of Action], vote no on the motion to disapprove and no on a veto override vote if necessary. I firmly believe that effective implementation of the JCPOA, bolstered by other U.S. policies, including a strong deterrence policy of the U.S. and our partners, will be in our national security interest," Casey said. "This agreement will substantially constrain the Iranian nuclear program for its duration, and compared with all realistic alternatives, it is the best option available to us at this time."

Casey released a 17-page analysis outlining his views on the international agreement, also talking to the Philadelphia Inquirer about his decision ahead of his public announcement.

The momentum is clearly on the side of supporters, as several House Democrats also made their support known Monday and Tuesday. That includes Democratic Rep. Elijah E. Cummings of Maryland.

"The long-standing, non-partisan and publicly-declared foreign policy commitment of the United States is clear. We will do whatever is required to prevent Iran from possessing nuclear weapons. Our nation has not ruled out any option that may be required to achieve this objective, including the use of military force," Cummings said. "Where the security interests of the United States and our allies are concerned, any alternative to the JCPOA must be judged against the real and tangible gains achieved by the JCPOA."

Neither of Maryland's Democratic senators have yet announced their positions, though Foreign Relations Ranking Member Benjamin L. Cardin has been speaking with constituents including college students.

"Congress presently faces a solemn charge to fulfill its oversight responsibilities and to conduct a thorough and rigorous review of the JCPOA. Each member of Congress must make a personal and very individual decision on whether he or she believes the agreement will keep Iran from becoming a nuclear weapon state and further the national security and foreign policy interests of the United States. Today's discussion with students at Johns Hopkins University represented an important part of my deliberations," Cardin said in a statement after an event in Baltimore.